Flange connection structure and sealing knowledge

The flange connection structure is an assembly consisting of a pair of flanges, several bolts, nuts and a gasket. It is an assembly drawing of the overall structure of the pipe flange connection. In practical applications, it is rare for pressure vessels to fail to seal flanges due to strength damage to the connecting parts or the connected parts. Leakage is more likely to occur due to poor sealing. Therefore, the main problem to be solved in the design of flange connection is to prevent medium leakage.

The principle of flange sealing is: the flange compresses the gasket between the sealing surfaces under the action of bolt pretightening force. The pressure (compression stress) exerted on the unit area must reach a certain value to cause the gasket to deform and be compacted. The micro-gaps formed by mechanical processing on the sealing surface are filled to form an initial sealing condition. The required compression stress is called the gasket sealing specific pressure, expressed in y, and the unit is MPa. The sealing specific pressure mainly depends on the gasket material. Obviously, when the gasket material is determined, the wider the gasket, the greater the preload force required to ensure the proper specific pressure, and thus the larger the size of the bolts and flanges, so the flange connection The middle gasket should not be too wide, nor should the entire flange surface be covered with gaskets. When the equipment or pipeline is in working condition, the axial force formed by the internal pressure of the medium causes the bolts to stretch, and the flange sealing surfaces move in the direction of separation from each other, reducing the compressive stress between the sealing surface and the gasket. If the gasket has sufficient resilience, the recovery of the compression deformation can compensate for the deformation of the bolt and sealing surface, so that the preload sealing specific pressure value is at least reduced to a certain value (this specific pressure value is called the working sealing ratio pressure), a good sealing state can be maintained between the flange sealing surfaces. On the contrary, if the resilience of the gasket is insufficient, the preload sealing specific pressure drops below the working sealing specific pressure, or even a gap reappears at the seal, the seal will fail. Therefore, in order to achieve sealing at the flange joint, the deformation of each part of the sealing assembly must be adapted to the sealing conditions under operating conditions. Even if the sealing element is under operating pressure, it still maintains a certain residual pressing force. To this end, both the bolts and the flange must have sufficient strength and rigidity to prevent the bolts from excessive deformation under the axial force caused by the internal pressure of the container.